1. Field of the Invention
The present invention relates to an electron beam exposure mask and a method for manufacturing the electron beam exposure mask and more particularly to the electron beam exposure mask and the method for manufacturing the electron beam exposure mask capable of forming fine patterns without losing mechanical strength.
2. Description of the Related Art
In manufacturing a semiconductor device represented by a LSI (Large-Scale Integrated)circuit, a lithography technology is essential in order to pattern various kinds of films, including insulation films such as a silicon oxidation film and a silicon nitride film formed on a semiconductor substrate and conductive films such as an aluminum alloy film and a copper alloy film, into desired shapes.
Conventionally, in this lithography technology, a photolithography technology is widely applied, in which a photoresist film is formed by coating photoresist having photosensitivity for ultraviolet rays, ultraviolet rays are irradiated (exposed) onto the photoresist film through a mask pattern, an ultraviolet ray irradiation area is made soluble (a positive type) or an ultraviolet ray non-irradiation area is made soluble (a negative type).
Now, as integration is improved with sophistication of the LSI, a lithography technology capable of further fine-processing is required. With this requirement, an electron beam lithography technology has been developed in which an electron beam of a wavelength shorter than that of the ultraviolet ray is used as an exposure medium.
In this electron beam lithography technology, an electron beam resist being photosensitive to an electron beam is used, and a desired pattern is represented by irradiating and exposing the electron beam to the electron beam resist. When the desired pattern is represented on the electron beam resist, a stencil mask, namely, an aperture mask (hereafter, called an electron beam exposure mask) is used. For the electron beam exposure mask, a material efficient in electron dispersion and in absorption and suitable for a fine process is used and generally a semiconductor film such as a silicon film is used.
FIG. 3 is a sectional view showing a conventional structure of an electron beam exposure mask.
An electron beam exposure mask 51, as shown in FIG. 3, is provided with a substrate portion 52 formed from a silicon single crystal or a like and provided with an aperture 53 and a thin film portion 54 supported by the substrate portion 52.
The thin film portion 54 is provided with a semiconductor active film 56 formed from a silicon single crystal through an buried insulation film 55 formed from a silicon oxide film or a like. The semiconductor active film 56 is provided with a pattern portion 57 provided with apertures 58 conducting to the semiconductor active film 56.
Here, the aperture 53 of the substrate portion 52 and the apertures 58 of the semiconductor active film 56 become electron beam passages during the electron beam exposure.
Explanations will be given of a method of manufacturing an electron beam exposure mask with reference to FIGS. 4A, 4B, 4C, 4D and 4E in accordance with a procedure.
First, as shown in FIG. 4A, a semiconductor substrate 60 formed from a silicon single crystal is used and an etching mask 61 formed from silicon oxide film, a silicon nitride film or a like is formed on a reverse of the semiconductor substrate 60 by a CVD (Chemical Vapor Deposition) process or a like.
Second, by applying a known SIMOX (Separation by IMplanted OXygen) technology to an obverse of the semiconductor substrate 60, oxygen ions are implanted to form the buried insulation film 55 of silicon oxide. The semiconductor active film 56 separated from the semiconductor substrate 60 by the buried insulation film 55 is formed.
Third, as shown in FIG. 4C, by applying a known photolithography process, necessary areas in the obverse of the semiconductor active film 56 are covered with photoresist film 62 and then dry etching is executed using the photoresist film 62 as a mask in order to form the semiconductor active film 56 in a desired shape, namely, in order to execute patterning. With this process, the pattern portion 57 of a desired shape having the apertures 58 is formed.
Fourth, after selectively etching the buried insulation film 55 exposed in the apertures 58, as shown in FIG. 4D, necessary areas in the etching mask are covered with photoresist film 63 and then dry etching is executed using the photoresist film 63 as a mask in order to form the etching mask 61 in a desired shape, namely, in order to execute patterning.
Fifth, after removing the photoresist film 63, wet etching is applied to the reverse of the semiconductor substrate 60 using the etching mask 61 as a mask and the semiconductor substrate 60 is selectively etched to form the apertures 53.
Finally, the etching mask 61 and the buried insulation film 55 exposed in the apertures 53 are removed by dry etching, and thereby the electron beam exposure mask 51 shown in FIG. 3 is completed.
Now, in a conventional electron beam exposure mask, there is a problem in that it is difficult to change a pattern accuracy partially since the semiconductor active film forming a pattern portion of a film portion supported by a substrate is formed wholly in a same film thickness.
In other words, concerning the electron beam exposure mask, though there is a case in that a pattern accuracy is changed partially on one mask and a fine pattern is formed on only a part of the mask according to a design rule, a film thickness of the above-mentioned semiconductor active film must be made thinner as to a processing precision to form such fine pattern.
However, when the film thickness of the semiconductor active film is made thin, mechanical strength of a mask deteriorates accordingly and a mask tolerance deteriorates. Therefore, the film thickness of the semiconductor active film must be thick to improve the mechanical strength of the mask.
For example, when the semiconductor active film is optimized to make a film thick in order to obtain mechanical strength, an aspect ratio becomes large in areas requiring a fine pattern. As a result, it is difficult to form fine apertures since a processing precision lacks. On the contrary, when the semiconductor active film is optimized to make a film thin, a fine pattern can be formed easily. However, the mechanical strength deteriorates since the whole mask becomes thin.
As above described, in manufacturing the electron beam exposure mask, forming the fine pattern is contrary to improving mechanical strength. Conventionally, since a film thickness of a semiconductor active film in which a pattern is formed is set to an identical thickness, there is a limitation in that a mask can be manufactured only from the viewpoint of forming the fine pattern or improving the mechanical strength.
Further, conventionally, instead of the semiconductor substrate, an SOI (Silicon On Insulator) substrate being two laminated substrates is manufactured. However, these two substrates are laminated under high tension, therefore, a mask is flexible under tension when the mask is made thinner. In addition, there are cases in that evenness during laminating deteriorates and in that since voids are apt to occur, etching liquid seeps in the voids in the manufacturing process and thereby the pattern is broken.
In view of the above, it is an object of the present invention to provide an electron beam exposure mask and a method of manufacturing the electron beam exposure mask, in which forming a fine pattern is compatible with improving mechanical strength.
According to a first aspect of the present invention, there is provided an electron beam exposure mask provided with a substrate portion, a thin film portion supported by the substrate portion, and a pattern portion formed into a desired shape in a semiconductor film formed through a buried insulation film in the thin film portion: wherein a first semiconductor film and a second semiconductor film thicker than the first semiconductor film are formed in the thin film portion; a fine pattern portion having small-gauge apertures is formed in the first semiconductor film; and a coarse pattern portion having large-gauge apertures is formed in the second semiconductor film.
In the foregoing first aspect, a preferable mode is one wherein the first semiconductor film is formed through a first buried insulation film and the second semiconductor film is formed through a second buried insulation film thinner than the first buried insulation film in the substrate portion.
In the foregoing, a preferable mode is one wherein an aperture conductive to the small-gauge apertures and conductive to the large-gauge apertures is formed in the substrate portion.
According to a second aspect of the present invention, there is provided a method of manufacturing an electron beam exposure mask including: a first semiconductor film forming step of forming an etching mask on:an obverse of a semiconductor substrate and forming an insulation film on a reverse of the semiconductor substrate and of forming a semiconductor film separated from the semiconductor substrate through a buried insulation film; a second semiconductor film forming step of increasing a thickness of the buried insulation film partially to divide the buried insulation film into a first buried insulation film and a second buried insulation film thinner than the first buried insulation film and of forming a first semiconductor film on the first buried insulation film and forming a second semiconductor film thicker than the first semiconductor film on the second buried insulation film; a pattern forming step of forming a fine pattern portion having small-gauge apertures in the first semiconductor film and forming a coarse pattern portion having large-gauge apertures in second semiconductor film; an etching mask patterning step of patterning the etching mask in a desired shape; and a semiconductor substrate etching step of selectively etching the reverse of the semiconductor substrate using the etching mask as a mask to form an aperture conductive to the small-gauge apertures and the large-gauge apertures.
In the foregoing, a preferable mode is one further including an etching step of etching the first buried insulation film and the second buried insulation film exposed to the etching mask and exposed in the aperture.
In the foregoing, a preferable mode is one wherein oxygen ions are implanted to form the buried insulation film in the first semiconductor forming step and to form the first buried insulation film and second buried insulation film in the second semiconductor forming step.
In the foregoing, a preferable mode is one wherein a SIMOX (Separation by IMplanted OXygen) technology is applied to the first semiconductor film forming step and to the second semiconductor film forming step.
In the foregoing, a preferable mode is one wherein a silicon nitride film or a silicon oxide film is used as the etching mask.
According to a third aspect of the present invention, there is provided an electron beam exposure mask including a substrate portion, a thin film portion supported by the substrate portion and a pattern portion formed into a desired shape in a semiconductor film formed through a buried insulation film in the thin film portion, the electron beam exposure mask including: a first semiconductor film formed in the thin film portion; a second semiconductor film thicker than the first semiconductor film in the thin film portion; a fine pattern portion having small-gauge apertures in the first semiconductor film; and a coarse pattern portion having large-gauge apertures in the second semiconductor film.
According to a fourth aspect of the present invention, there is provided a media for storing a program for manufacturing an electron beam exposure mask, the program including: a first semiconductor film forming step of forming an etching mask on an obverse of a semiconductor substrate and forming an insulation film on a reverse of the semiconductor substrate and of forming a semiconductor film separated from the semiconductor substrate through the buried insulation film; a second semiconductor film forming step of increasing a thickness of the buried insulation film partially to divide the buried insulation film into a first buried insulation film and a second buried insulation film thinner than the first buried insulation film and of forming a first semiconductor film on the first buried insulation film and forming a second semiconductor film thicker than the first semiconductor film on the second buried insulation film; a pattern forming step of forming a fine pattern portion having small-gauge apertures in the first semiconductor film and forming a coarse pattern portion having large-gauge apertures in the second semiconductor film; an etching mask patterning step of patterning the etching mask in a desired shape; and a semiconductor substrate etching step of selectively etching the reverse of the semiconductor substrate using the etching mask as a mask to form an aperture conductive to the small-gauge apertures and the large-gauge apertures.